US7672285B2 - Method and apparatus for minimizing co-channel interference by scrambling - Google Patents

Method and apparatus for minimizing co-channel interference by scrambling Download PDF

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US7672285B2
US7672285B2 US11/009,333 US933304A US7672285B2 US 7672285 B2 US7672285 B2 US 7672285B2 US 933304 A US933304 A US 933304A US 7672285 B2 US7672285 B2 US 7672285B2
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channels
channel
frames
header
communication system
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US20050286405A1 (en
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Feng-Wen Sun
Lakshmi Iyer
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DTVG Licensing Inc
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DTVG Licensing Inc
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Assigned to DIRECTV GROUP, INC., THE reassignment DIRECTV GROUP, INC., THE ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: IYER, LAKSHMI, SUN, FENG-WEN
Priority to US11/009,333 priority Critical patent/US7672285B2/en
Priority to JP2007519222A priority patent/JP4777982B2/ja
Priority to AT05753920T priority patent/ATE539507T1/de
Priority to EP05753920A priority patent/EP1766818B1/de
Priority to CN2010101678428A priority patent/CN101834653B/zh
Priority to CA2572431A priority patent/CA2572431C/en
Priority to CN2005800267100A priority patent/CN1993914B/zh
Priority to HK07109050.1A priority patent/HK1104394B/xx
Priority to PCT/US2005/018564 priority patent/WO2006007204A2/en
Priority to KR1020077002090A priority patent/KR100877241B1/ko
Publication of US20050286405A1 publication Critical patent/US20050286405A1/en
Assigned to DTVG LICENSING, INC. reassignment DTVG LICENSING, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: THE DIRECTV GROUP, INC.
Priority to US12/692,344 priority patent/US8325699B2/en
Publication of US7672285B2 publication Critical patent/US7672285B2/en
Application granted granted Critical
Priority to HK11102054.6A priority patent/HK1148129B/xx
Priority to US13/528,347 priority patent/US9537689B2/en
Priority to US13/692,793 priority patent/US9060369B1/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H04W72/044—Wireless resource allocation based on the type of the allocated resource
    • H04W72/0466—Wireless resource allocation based on the type of the allocated resource the resource being a scrambling code
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/18578—Satellite systems for providing broadband data service to individual earth stations
    • H04B7/1858—Arrangements for data transmission on the physical system, i.e. for data bit transmission between network components
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/16—Code allocation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/541—Allocation or scheduling criteria for wireless resources based on quality criteria using the level of interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H04B1/7103—Interference-related aspects the interference being multiple access interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/10—Code generation
    • H04J13/102—Combining codes

Definitions

  • the present invention relates to communication systems, and more particularly to combating signal interference.
  • Satellite communication systems have emerged as a viable solution for supporting such broadband services.
  • power and bandwidth efficient modulation and coding are highly desirable for satellite communications systems to provide reliable communication across noisy communication channels.
  • Receiver performance is negatively impacted by co-channel interference.
  • co-channel interference occurs largely from frequency-reuse, as spectral allocation of frequencies is finite and expensive.
  • the co-channel interference may stem from transmission of other system operators, a satellite operating in adjacent orbital slots, or other spot beams in a spot beam satellite system.
  • the cross-correlations between co-channel frames are periodic in nature.
  • Each of these frames includes a header and a pilot sequence for synchronization of carrier phase and carrier frequency.
  • Non-header portions of the frames are scrambled according to respective different scrambling sequences to minimize interference between the co-channels.
  • different initialization seeds are supplied to a Gold sequence generator for each of the co-channels to produce the different scrambling sequences.
  • a method for minimizing co-channel interference in a communication system includes assigning a first scrambling sequence, associated with a header or a pilot sequence of a first frame, to a first co-channel.
  • the method also includes assigning a second scrambling sequence, associated with a header or a pilot sequence of a second frame, to a second co-channel that is adjacent to the first co-channel.
  • the non-header portions of the frames are scrambled according to the respective different scrambling sequences.
  • an apparatus for minimizing co-channel interference in a communication system includes a scrambler configured to assign a first scrambling sequence, associated with a header or a pilot sequence of a first frame, to a first co-channel.
  • the scrambler assigns a second scrambling sequence, associated with a header or a pilot sequence of a second frame, to a second co-channel that is adjacent to the first co-channel.
  • the non-header portions of the frames are scrambled according to the respective scrambling sequences.
  • a method for communicating in a radio communication system includes transmitting a plurality of frames over different communication channels established over the radio communication system.
  • the communication channels are adjacent co-channels.
  • Each of the frames includes a header and a pilot sequence for synchronization of carrier phase and carrier frequency, and non-header portions of the frames are scrambled according to respective different scrambling sequences to minimize interference between the co-channels.
  • an apparatus for communicating in a radio communication system includes a transmitter configured to transmit a plurality of frames over different communication channels established over the radio communication system, wherein the communication channels are adjacent co-channels.
  • Each of the frames includes a header and a pilot sequence for synchronization of carrier phase and carrier frequency, and non-header portions of the frames are scrambled according to respective different scrambling sequences to minimize interference between the co-channels.
  • method for communicating in a radio communication system includes receiving a plurality of frames over different communication channels established over the radio communication system.
  • the communication channels are adjacent co-channels.
  • Each of the frames includes a header and a pilot sequence for synchronization of carrier phase and carrier frequency, and non-header portions of the frames are scrambled according to respective different scrambling sequences to minimize interference between the co-channels.
  • an apparatus for communicating in a radio communication system includes a receiver configured to receive a plurality of frames over different communication channels established over the radio communication system, wherein the communication channels are adjacent co-channels.
  • Each of the frames includes a header and a pilot sequence for synchronization of carrier phase and carrier frequency, and non-header portions of the frames are scrambled according to respective different scrambling sequences to minimize interference between the co-channels.
  • FIG. 1 is a diagram of a digital broadcast system capable of minimizing co-channel interference, according to an embodiment of the present invention
  • FIG. 2 is a diagram of an exemplary transmitter employed in the digital transmission facility of the system of FIG. 1 ;
  • FIG. 3 is a diagram of an exemplary digital modem in the system of FIG. 1 ;
  • FIG. 4 is a diagram of an exemplary frame structure used in the system of FIG. 1 ;
  • FIGS. 5A and 5B are, respectively, a diagram of a scrambler for isolating co-channel interference and a diagram of a Gold sequence generator for outputting Gold codes used to construct scrambling codes, according to various embodiments of the present invention
  • FIG. 6 is a diagram showing the periodic nature of the cross-correlation between co-channel frames, in accordance with an embodiment of the present invention.
  • FIG. 7 is a diagram of an exemplary Gold sequence generator used in the scrambler of FIG. 6 ;
  • FIG. 8 is a flowchart of a process for generating different physical layer sequences, according to an embodiment of the present invention.
  • FIG. 9 is a flowchart of process for generating scrambled physical headers, according to an embodiment of the present invention.
  • FIGS. 10 and 11 are tables showing the worst-case cross-correlations of pilot-segments for each pair of co-channels for determining the initialization seeds of the m-generator of FIG. 7 ;
  • FIG. 12 is a diagram of a hardware platform that can perform the various processes for isolating co-channel interference, in accordance with embodiments of the present invention.
  • FIG. 1 is a diagram of a digital broadcast system capable of minimizing co-channel interference, according to an embodiment of the present invention.
  • the digital communications system 100 includes a digital transmission facility 101 that generates signal waveforms for broadcast across a communication channel 103 to one or more digital modems 105 .
  • the communication system 100 is a satellite communication system that supports, for example, audio and video broadcast services as well as interactive services.
  • Interactive services include, for example, electronic programming guides (EPGs), high-speed internet access, interactive advertising, telephony, and email services. These interactive services can also encompass such television services as Pay Per View, TV Commerce, Video On Demand, Near Video On Demand and Audio On Demand services.
  • the modems 105 are satellite modems.
  • continuous mode modems 105 are widely used. Codes that perform well in low signal-to-noise (SNR) environments are at odds with these modems with respect to synchronization (e.g., carrier phase and carrier frequency). Physical layer header and/or pilot symbols can be used for such synchronization. Accordingly, an important consideration with respect to system performance is that of co-channel interference on physical layer header and/or pilot symbols. Because physical layer header and/or pilots are used for acquiring and/or tracking carrier phase, carrier frequency, such interference can degrade receiver performance.
  • SNR signal-to-noise
  • the modems 105 achieve carrier synchronization by examining the preambles and/or unique words (UW) that are embedded in broadcast data frame structures (shown in FIG. 4 ), thereby reducing the use of additional overhead specifically designated for training purposes.
  • the digital modems 105 are more fully described below with respect to FIG. 3 .
  • the transmission facility 101 produces a discrete set of possible messages representing media content (e.g., audio, video, textual information, data, etc.); each of the possible messages has a corresponding signal waveform. These signal waveforms are attenuated, or otherwise altered, by communications channel 103 . To combat the noise channel 103 , the transmission facility 101 utilizes Low Density Parity Check (LDPC) codes.
  • LDPC Low Density Parity Check
  • the LDPC codes that are generated by the transmission facility 101 enable high speed implementation without incurring any performance loss.
  • These structured LDPC codes output from the transmission facility 101 avoid assignment of a small number of check nodes to the bit nodes already vulnerable to channel errors by virtue of the modulation scheme (e.g., 8PSK).
  • Such LDPC codes have a parallelizable decoding process (unlike turbo codes), which advantageously involves simple operations such as addition, comparison and table look-up.
  • carefully designed LDPC codes do not exhibit any sign of error floor.
  • the transmission facility 101 generates, using a relatively simple encoding technique as explained below in FIG. 2 , LDPC codes based on parity check matrices (which facilitate efficient memory access during decoding) to communicate with the satellite modem 105 .
  • FIG. 2 is a diagram of an exemplary transmitter employed in the digital transmission facility of the system of FIG. 1 .
  • a transmitter 200 is equipped with an LDPC encoder 203 that accepts input from an information source 201 and outputs coded stream of higher redundancy suitable for error correction processing at the receiver 105 .
  • the information source 201 generates k signals from a discrete alphabet, X.
  • LDPC codes are specified with parity check matrices.
  • encoding LDPC codes require, in general, specifying the generator matrices. Even though it is possible to obtain generator matrices from parity check matrices using Gaussian elimination, the resulting matrix is no longer sparse and storing a large generator matrix can be complex.
  • Encoder 203 generates signals from alphabet Y to a modulator 205 using a simple encoding technique that makes use of only the parity check matrix by imposing structure onto the parity check matrix. Specifically, a restriction is placed on the parity check matrix by constraining certain portion of the matrix to be triangular. Such a restriction results in negligible performance loss, and therefore, constitutes an attractive trade-off.
  • the construction of such a parity check matrix is described more fully described in a co-pending patent application filed Jul. 3, 2003, and entitled, “Method and System for Providing Low Density Parity Check (LDPC) Encoding” (Ser. No. 10/613,823); the entirety of which is incorporated herein by reference.
  • LDPC Low Density Parity Check
  • Modulator 205 maps the encoded messages from encoder 203 to signal waveforms that are transmitted to a transmit antenna 207 , which emits these waveforms over the communication channel 103 . Accordingly, the encoded messages are modulated and distributed to a transmit antenna 207 . The transmissions from the transmit antenna 207 propagate to a digital modem, as discussed below. In the case of a satellite communication system, the transmitted signals from the antenna 207 are relayed via a satellite.
  • the transmitter 200 further includes a scrambler 209 for altering symbols for transmission as to minimize co-channel interference, as more fully described below.
  • FIG. 3 is a diagram of an exemplary digital modem in the system of FIG. 1 .
  • the digital modem 300 as a modulator/demodulator, supports both transmission and reception of signals from the transmitter 200 .
  • the modem 300 has a front-end module 301 that provides filtering and symbol timing synchronization of the LDPC encoded signals received from antenna 303 , a carrier synchronization module 302 that provides frequency and phase acquisition and tracking of the signals output from the front-end module 301 .
  • a demapper 305 performs demapping of received signals output from the carrier synchronization module 302 .
  • the signals are forwarded to a LDPC decoder 307 , which attempts to reconstruct the original source messages by generating messages, X′.
  • the modem 300 utilizes a LDPC encoder 309 to encode input signals.
  • the encoded signals are then modulated by a modulator 311 , which can employ a variety of modulation schemes—e.g., Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 8PSK, 16 Amplitude Phase Shift Keying (APSK), 32APSK, a high order Quadrature Amplitude Modulation (QAM), or other high order modulation schemes.
  • BPSK Binary Phase Shift Keying
  • QPSK Quadrature Phase Shift Keying
  • 8PSK 8PSK
  • APSK 16 Amplitude Phase Shift Keying
  • 32APSK 32APSK
  • QAM Quadrature Amplitude Modulation
  • FIG. 4 is a diagram of an exemplary frame structure used in the system of FIG. 1 .
  • an LDPC coded frame 400 which can support, for example, satellite broadcasting and interactive services, is shown.
  • the frame 400 includes a Physical Layer Header (denoted “PLHEADER”) 401 and occupies one slot, as well as other slots 403 for data or other payload.
  • PHEADER Physical Layer Header
  • the frame 400 utilizes a pilot block 405 to aid synchronization of carrier phase and frequency. It is noted that the pilot block 405 is optional, and is inserted via a pilot insertion process.
  • the pilot block (or pilot sequence) 405 which represents a Unique Word (UW), can be inserted anywhere along the frame 400 .
  • UW Unique Word
  • the pilot insertion process inserts pilot blocks every 1440 symbols.
  • the pilot block includes 36 pilot symbols.
  • the first pilot block is thus inserted 1440 symbols after the PLHEADER, the second pilot block is inserted after 2880 symbols, and etc. If the pilot block position coincides with the beginning of the next PLHEADER, then the pilot block is not inserted.
  • the above pilot insertion process is further detailed in co-pending application, entitled “Method and Apparatus for Providing Carrier Synchronization in Digital Broadcast and Interactive Systems” (filed May 10, 2004; Ser. No. 10/842,325); which is incorporated herein in its entirety.
  • the carrier synchronization module 302 ( FIG. 3 ), according to an embodiment of the present invention, utilizes the PLHEADER 401 and/or UWs 405 for carrier frequency and phase synchronization.
  • the FEC coded data which contains known data symbols (e.g., the PLHEADER 401 ) are ignored in continuous mode modems. That is, the PLHEADER 401 and/or UWs 405 are used for carrier synchronization, i.e., for assisting with the operation of frequency acquisition and tracking, and phase tracking loop.
  • the PLHEADER 401 and UWs 405 are considered “training” or “pilot” symbols, and constitute, individually or collectively, a training block.
  • the pilot sequence 405 is a 36-symbol long segment (with each symbol being (1+j)/ ⁇ square root over (2) ⁇ ); that is, 36 symbols (PSK).
  • the pilot sequence 405 can be inserted after 1440 symbols of data.
  • the PLHEADER 401 can have 64 possible formats depending on the modulation, coding and pilot configuration.
  • the non-header portion 407 of the frame 400 is scrambled.
  • the scrambling process is further explained with respect to FIGS. 5A , 5 B, 8 and 9 .
  • the scrambled pilot sequence is also denoted as a “pilot-segment” of the frame 400 .
  • the frame 400 exhibits a structure for an 8PSK-modulated frame, when transmitting in the long-frame mode (e.g., 64800 data bits/frame), a QPSK-modulated frame can contain 22 pilot-segments.
  • the frame 400 is described with respect to a structure that supports satellite broadcasting and interactive services (and compliant with the Digital Video Broadcast (DVB)—S2 standard), it is recognized that the carrier synchronization techniques of the present invention can be applied to other frame structures.
  • DVD Digital Video Broadcast
  • FIG. 5A is a diagram of a scrambler for isolating co-channel interference, according to an embodiment of the present invention.
  • a scrambling code is a complex sequence that can be constructed from a Gold code, according to one embodiment of the present invention. That is, a scrambler 209 generates a scrambling sequence Rn(i).
  • Table 1 defines how the scrambling sequence Rn(i) scrambles the frame using the scrambler 209 , according to the scrambler logic of FIG. 7 . In particular, Table 1 shows the mapping of an input symbol to an output symbol based on the output of the scrambler 209 .
  • Different Gold sequences can be generated by using different seeds for either of the two m-sequence generators. By using different seeds for different services, the mutual interference can be reduced.
  • the 90 symbol physical layer header 401 can remain constant for a particular physical channel.
  • the Gold sequence is reset at the beginning of each frame, and thus, the scrambled pilots are periodical as well with a period equal to the frame length. Because the information carrying data in a frame varies and appears to be random, the co-channel interference is random and degrades the operating signal-to-noise ratio. However, due to the nature of time-invariance of the physical layer header 401 and the pilot block 405 , the carrier and phase estimation is skewed for a receiver depending on these pilots and physical layer header for such acquisition and tracking. This will degrade the performance beyond those of signal-to-noise ratio degradation associated with random data.
  • the scrambler 209 utilized different scrambling sequences (n in number) to further isolate the co-channel interference.
  • Each scrambling sequence, or pilot sequence corresponds to a different seed n.
  • 17 possible configurations are provided, as shown in Table 2 below. In each configuration, one scrambling sequence is provided for the physical layer header and one for the pilots. Different pilots are specified in terms of different seed of the Gold sequences.
  • FIG. 5B provides a diagram of a Gold sequence generator for outputting Gold codes used to construct scrambling codes, in accordance with an embodiment of the present invention.
  • a Gold Sequence Generator 500 employs two Pseudo-Noise (PN) Sequence Generators 501 , 503 to generate a “preferred pair” of sequences.
  • the “preferred pair” can be specified by “preferred polynomials” (as seen in the scrambler of FIG. 7 ).
  • the outputs of these PN Sequence Generators 501 , 503 are fed to an XOR logic 505 , which performs an Exclusive-OR function on the output sequences to produce a Gold sequence.
  • the Gold Sequence Generator 500 generates Gold sequences from a large class of sequences that exhibit good periodic cross-correlation properties.
  • G(u,v) contains N+2 sequences of period N.
  • Gold sequences have the property that the cross-correlation between any two, or between shifted versions of them, assumes one of three values: ⁇ t(n), ⁇ 1, or t(n) ⁇ 2, where
  • the scrambling mechanism of the scrambler 209 advantageously reduces the signaling by associating one by one between the physical layer signaling and the different seeds representing different Gold sequences.
  • Table 2 enumerates the selection of the scrambling sequence for the physical layer header, in octal format.
  • the co-channel interference consists only of terms corresponding to the cross-correlation between the pilot-segments of the channels.
  • the data of one channel and pilot-segment on the other channel are also uncorrelated.
  • the correlation may be complete or partial.
  • the correlation C XY (n) of the pilot-segments x(n) and y(n) is expressed in Equation 3, where the sum is over the number of overlapping symbols.
  • FIG. 7 is a diagram of an exemplary Gold sequence generator used in the scrambler of FIG. 6 .
  • a Gold sequence generator 700 employs the preferred polynomials of 1+X 7 +X 18 and 1+Y 5 +Y 7 +Y 10 +Y 18 .
  • the seeds in Tables 3 and 4 can be programmed into an m-sequence generator 701 .
  • the Gold code sequence numbers “n” corresponding to the initialization are also listed in Table 3.
  • the seeds are generated, according to one embodiment of the present invention, using a sub-optimal search algorithm that minimizes the worst cross-correlation between every pair of the co-channel pilot-segments.
  • FIGS. 10 and 11 The worst case correlations between any two of the listed co-channels of Tables 3 and 4 are given in FIGS. 10 and 11 , respectively.
  • the maximum cross-correlation is seen in FIG. 10 to be ⁇ 2.78 dB (highlighted in bold font).
  • this maximum cross-correlation occurs at ⁇ 2.92 dB. It is observed that, although the Gold sequences themselves have good cross-correlation properties, the pilot-segments can exhibit poor cross-correlation characteristics. This is due to the fact that the segments are only 36-symbols long and the seed-selection procedure is constrained by the worst cross-correlation.
  • FIG. 8 is a flowchart of a process for generating different physical layer sequences, according to an embodiment of the present invention.
  • step 801 different initialization seeds are assigned to the respective co-channels.
  • Gold sequences are generated based on the seeds, per step 803 .
  • a scrambling sequence is then constructed, as in step 805 , from the Gold sequence for each different service.
  • step 807 the physical layer sequences are output by the scrambler 209 ( FIG. 2 ).
  • FIG. 9 is a flowchart of process for generating scrambled physical headers, according to an embodiment of the present invention.
  • the transmitter 200 receives input symbols associated with the physical header or pilot sequence, as in step 901 .
  • the transmitter maps the input symbols according to a scrambling sequence generated by the scrambler 209 .
  • the output symbols are then generated, per step 905 .
  • the transmitter outputs a frame with a scrambled physical and/or scrambled pilot sequence (step 907 ).
  • FIG. 12 illustrates exemplary hardware upon which an embodiment according to the present invention can be implemented.
  • a computing system 1200 includes a bus 1201 or other communication mechanism for communicating information and a processor 1203 coupled to the bus 1201 for processing information.
  • the computing system 1200 also includes main memory 1205 , such as a random access memory (RAM) or other dynamic storage device, coupled to the bus 1201 for storing information and instructions to be executed by the processor 1203 .
  • Main memory 1205 can also be used for storing temporary variables or other intermediate information during execution of instructions by the processor 1203 .
  • the computing system 1200 may further include a read only memory (ROM) 1207 or other static storage device coupled to the bus 1201 for storing static information and instructions for the processor 1203 .
  • ROM read only memory
  • a storage device 1209 such as a magnetic disk or optical disk, is coupled to the bus 1201 for persistently storing information and instructions.
  • the computing system 1200 may be coupled via the bus 1201 to a display 1211 , such as a liquid crystal display, or an active matrix display, for displaying information to a user.
  • a display 1211 such as a liquid crystal display, or an active matrix display
  • An input device 1213 such as a keyboard including alphanumeric and other keys, may be coupled to the bus 1201 for communicating information and command selections to the processor 1203 .
  • the input device 1213 can include a cursor control, such as a mouse, a trackball, or cursor direction keys, for communicating direction information and command selections to the processor 1203 and for controlling cursor movement on the display 1211 .
  • the processes of FIGS. 8 and 9 can be provided by the computing system 1200 in response to the processor 1203 executing an arrangement of instructions contained in main memory 1205 .
  • Such instructions can be read into main memory 1205 from another computer-readable medium, such as the storage device 1209 .
  • Execution of the arrangement of instructions contained in main memory 1205 causes the processor 1203 to perform the process steps described herein.
  • processors in a multi-processing arrangement may also be employed to execute the instructions contained in main memory 1205 .
  • hard-wired circuitry may be used in place of or in combination with software instructions to implement the embodiment of the present invention.
  • reconfigurable hardware such as Field Programmable Gate Arrays (FPGAs) can be used, in which the functionality and connection topology of its logic gates are customizable at run-time, typically by programming memory look up tables.
  • FPGAs Field Programmable Gate Arrays
  • the computing system 1200 also includes at least one communication interface 1215 coupled to bus 1201 .
  • the communication interface 1215 provides a two-way data communication coupling to a network link (not shown).
  • the communication interface 1215 sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information.
  • the communication interface 1215 can include peripheral interface devices, such as a Universal Serial Bus (USB) interface, a PCMCIA (Personal Computer Memory Card International Association) interface, etc.
  • USB Universal Serial Bus
  • PCMCIA Personal Computer Memory Card International Association
  • the processor 1203 may execute code that is being received over the communication interface 1215 and/or store the code in the storage device 1209 , or other non-volatile storage for later execution. In this manner, the computing system 1200 may obtain application code in the form of a carrier wave.
  • Non-volatile media include, for example, optical or magnetic disks, such as the storage device 1209 .
  • Volatile media include dynamic memory, such as main memory 1205 .
  • Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise the bus 1201 . Transmission media can also take the form of acoustic, optical, or electromagnetic waves, such as those generated during radio frequency (RF) and infrared (IR) data communications.
  • RF radio frequency
  • IR infrared
  • Computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, CDRW, DVD, any other optical medium, punch cards, paper tape, optical mark sheets, any other physical medium with patterns of holes or other optically recognizable indicia, a RAM, a PROM, and an EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave, or any other medium from which a computer can read.
  • a floppy disk a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, CDRW, DVD, any other optical medium, punch cards, paper tape, optical mark sheets, any other physical medium with patterns of holes or other optically recognizable indicia, a RAM, a PROM, and an EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave, or any other medium from which a computer can read.
  • the instructions for carrying out at least part of the present invention may initially be borne on a magnetic disk of a remote computer.
  • the remote computer loads the instructions into main memory and sends the instructions over a telephone line using a modem.
  • a modem of a local system receives the data on the telephone line and uses an infrared transmitter to convert the data to an infrared signal and transmit the infrared signal to a portable computing device, such as a personal digital assistant (PDA) or a laptop.
  • PDA personal digital assistant
  • An infrared detector on the portable computing device receives the information and instructions borne by the infrared signal and places the data on a bus.
  • the bus conveys the data to main memory, from which a processor retrieves and executes the instructions.
  • the instructions received by main memory can optionally be stored on storage device either before or after execution by processor.
  • the various embodiments of the present invention provide an approach for minimizing co-channel interference in a digital broadcast and interactive system. It is recognized that the cross-correlations between co-channel frames are periodic in nature. Each of these frames includes a header and a pilot sequence for synchronization of carrier phase and carrier frequency. Non-header portions of the frames are scrambled according to respective different scrambling sequences to minimize interference between the co-channels. According to one embodiment of the present invention, different initialization seeds are supplied to a Gold sequence generator for each of the co-channels to produce the different scrambling sequences. The above arrangement advantageously reduces the impact of co-channel interference, thereby enhancing receiver performance.

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US11/009,333 US7672285B2 (en) 2004-06-28 2004-12-10 Method and apparatus for minimizing co-channel interference by scrambling
PCT/US2005/018564 WO2006007204A2 (en) 2004-06-28 2005-05-26 Method and apparatus for minimizing co-channel interference by scrambling
AT05753920T ATE539507T1 (de) 2004-06-28 2005-05-26 Verfahren und vrrichtung zur minimierung von cokanalstörungen durch verwürfelung
EP05753920A EP1766818B1 (de) 2004-06-28 2005-05-26 Verfahren und vrrichtung zur minimierung von cokanalstörungen durch verwürfelung
CN2010101678428A CN101834653B (zh) 2004-06-28 2005-05-26 通过加扰来最小化同信道干扰的方法和设备
CA2572431A CA2572431C (en) 2004-06-28 2005-05-26 Method and apparatus for minimizing co-channel interference by scrambling
CN2005800267100A CN1993914B (zh) 2004-06-28 2005-05-26 通过加扰来最小化同信道干扰的方法和设备
HK07109050.1A HK1104394B (en) 2004-06-28 2005-05-26 Method and apparatus for minimizing co-channel interference by scrambling
JP2007519222A JP4777982B2 (ja) 2004-06-28 2005-05-26 スクランブリングによって共チャネル干渉を最小化するための方法及び装置
KR1020077002090A KR100877241B1 (ko) 2004-06-28 2005-06-26 스크램블링에 의한 코채널 간섭을 최소화하기 위한 방법 및장치
US12/692,344 US8325699B2 (en) 2004-06-28 2010-01-22 Method and apparatus for minimizing co-channel interference by scrambling
HK11102054.6A HK1148129B (en) 2004-06-28 2011-03-01 Method and apparatus for minimizing co-channel interference by scrambling
US13/528,347 US9537689B2 (en) 2004-04-12 2012-06-20 Method and apparatus for identifying co-channel interference
US13/692,793 US9060369B1 (en) 2004-06-28 2012-12-03 Method and apparatus for minimizing co-channel interference by scrambling

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